Copolymer resin, preparation thereof, and photoresist using the same

ABSTRACT

The present invention relates to a copolymer resin for ultra-shortwave light source such as KrF or ArF, process for preparation thereof, and photoresist comprising the same resin. The copolymer resin according to the present invention is easily prepared by conventional radical polymerization due to the introduction of norbonyl(meth)acrylate unit to a structure of copolymer for photoresist. The resin has high transparency at 193 nm wavelength, provides increased etching resistance and enhanced adhesive strength due to a hydrophilic functional group in the norbonyl group, and shows excellent resolution of 0.15 μm in practical experiment of patterning.

BACKGROUND OF THE INVENTION

The present invention relates generally to a technique including aprocess and resulting structure for a copolymer resin for anultra-shortwave light source such as KrF or ArF. More specifically, itrelates to a copolymer resin, where a norbonyl(meth)acrylate unit isintroduced to a copolymeric structure for a photo resist. The photoresist can be used in a variety of lithography processes using a KrF(248 nm) or ArF (193) light source which is a light source to be appliedin next generation memory elements such as 1G or 4G DRAM integratedcircuit chips.

In general, characteristics such as etching resistance, adhesivenesswith low light absorption at 193 nm wavelength are often desired for acopolymer resin for ArF. The copolymer resin should also be developableby using, for example, a 2.38 wt % aqueous solution oftetramethylammonium hydroxide (TMAH). It is difficult, however, tosynthesize a copolymer resin satisfying some or all these desirablecharacteristics. Many researches have often focused on studies on anorbolac type resin as a material to increase transparency at 193 nmwavelength and increase etching resistance. Thus, attempts toemploy(meth)acrylate resins having high transparency, and to introducealicyclic compounds to resin side chains in order to overcomelimitations of deficient etching resistance, have been suggested. Forexample, IBM suggested the use of a copolymer resin represented byfollowing chemical formula I:

where R₁, R₂ and R₃ independently represent hydrogen or methyl.

The copolymer resin represented by chemical formula I unfortunately hasincreased hydrophobicity. The increased hydrophobicity occurs, in part,from introducing an alicyclic compound to the side chain, whichdecreases solubility in the developing solution and weakensadhesiveness, so that the compound can be contained in the copolymerresin composition in an amount not more than a certain level. It shouldbe noted that if the alicyclic compound is included at less than thecertain level, satisfactory etching resistance cannot generally beachieved. It has been found that, among the conventional alicyclicgroups on side chains, which are commonly known, the norbonyl oradmantyl group is effective in view of etching resistance. Theconventional copolymer resin including formula I has a severe limitationin that adhesive strength decreases by gaining hydrophobicity as thecontent of the cyclic compound in the resin composition increases.

From the above, it is seen that an improved photo resist that hasimproved characteristics is highly desirable.

SUMMARY OF THE INVENTION

The present inventors have performed intensive studies to overcome theabove problems encountered in conventional photo resist products, and asa result, they found a copolymer resin composition having hightransparency at 193 nm wavelength and high etching resistance.

In a specific embodiment, the present copolymer resin is prepared byradical polymerization techniques. These techniques include a variety ofsteps such as introducing norbonyl(meth)acrylate unit in a copolymerresin for photo resist. An adhesive strength of the resin can beincreased by introducing a hydrophilic group in norbonyl group. Asignificant difference of solubility to the developing solution betweenthe exposed region and non-exposed region can be provided through theprocesses of introducing a suitable protecting group, exposing, anddeprotecting by post-heating step.

In an alternative embodiment, the present invention provides a monomercomprising a 5-hydroxy-6-norbonyl(meth)acrylate derivative. In a furtherembodiment, the present invention provides a process for preparing themonomer. In still a further embodiment, the present invention provides acopolymer resin comprising 5-hydroxy-6-norbonyl (meth)acrylatederivative and a process for preparing the copolymer resin. Among otheraspects, the invention also provides photo resist comprising thecopolymer resin or resins. Still further, the present invention providesa process for manufacturing the photo resist and a semiconductor elementhaving a pattern formed by using the photo resist. These and otherembodiments will be described throughout the present specification andmore particularly below.

The present invention achieves these benefits in the context of knownprocess technology. However, a further understanding of the nature andadvantages of the present invention may be realized by reference to thelatter portions of the specification and attached drawings.

DETAILED DESCRIPTION OF THE INVENTION

In a specific embodiment, the present invention relates generally to acopolymer resin comprising 5-hydroxy-6-norbonyl(meth)acrylate derivativerepresented by chemical formula II:

where R represents 2-tert-butoxycarbonyl, 2-carboxylic,2-hydropyranyloxycarbonyl, 2-hydroxyfuranyloxycarbonyl or2-ethoxyethyloxycarbonyl; R₁ represents hydrogen or methyl.

The copolymer resin according to the present invention preferablyincludes copolymers represented by chemical formula III to VII.

(1)Poly[2-tert-butoxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-carboxylic-5-hydroxy-6-norbonyl(meth)acrylate] copolymer resin (Molecular Weight: 4,000 to 100,000)

[In the formula, R₁ and R₂ independently represent hydrogen or methyl,and x and y independently represent a mole fraction between 0.001 and0.99.]

(2)Poly[2-tert-butoxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-hydroxyethyl(meth)acrylicacid/(meth)acrylic acid] copolymer resin (Molecular Weight: 4,000 to10000)

[In the formula, R₁, R₂ and R₃ independently represent hydrogen ormethyl, and x, y and z independently represent a molar fraction between0.001 and 0.99.]

(3)Poly[2-hydroxypyranyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-hydroxyethyl(meth)acrylate/(meth)acrylicacid] copolymer resin (Molecular Weight: 4,000 to 100,000)

[In the formula, R₁, R₂ and R₃ independently represent hydrogen ormethyl, and x, y and z independently represent a mole fraction between0.001 and 0.99.]

(4)Poly[2-hydrofuranyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-hydroxyethyl(meth)acrylate/(meth)acrylicacid] copolymer resin (Molecular Weight: 4,000 to 100,000)

[In the formula, R₁, R₂ and R₃ independently represent hydrogen ormethyl, and x, y and z independently represent a mole fraction between0.001 and 0.99.]

(5)Poly[2-ethoxyethyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-hydroxyethyl(meth)acrylate/(meth)acrylicacid] copolymer resin (Molecular Weight: 4,000 to 100,000)

[In the formula, R₁, R₂ and R₃ independently represent hydrogen ormethyl, and x, y and z independently represent a mole fraction between0.001 and 0.99.]

The copolymer resin of formula III according to the present inventioncan be prepared by reacting 2-tert-butoxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate with 2-carboxylic-5-hydroxy-6-norbonyl (meth)acrylate inthe presence of a conventional polymerization initiator, as illustratedin reaction scheme I:

where R₁ and R₂ independently represent hydrogen or methyl.

The copolymer resin of formula IV according to the present invention canbe prepared by reacting 2-tert-butoxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate with 2-hydroxyethyl (meth)acrylate in the presence of aconventional polymerization initiator, as illustrated in reaction schemeII:

where R₁, R₂ and R₃ independently represent hydrogen or methyl.

The copolymer resin of formula V according to the present invention canbe prepared by reacting 2-hydroxypyranyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate and (meth)acrylic acid inthe presence of a conventional polymerization initiator, as illustratedin reaction scheme III:

wherein, R₁, R₂ and R₃ independently represent hydrogen or methyl.

The copolymer resin of formula VI according to the present invention canbe prepared by reacting 2-hydrofuranyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate and (meth)acrylic acid inthe presence of a conventional polymerization initiator, as illustratedin reaction scheme IV:

where R₁, R₂ and R₃ independently represent hydrogen or methyl.

The copolymer resin of formula VII according to the present inventioncan be prepared by reacting2-ethoxyethyloxycarbonyl-5-hydroxy-6-norbonyl (meth)acrylate,2-hydroxyethyl (meth)acrylate and (meth)acrylic acid in the presence ofa conventional polymerization initiator, as illustrated in reactionscheme V:

wherein R₁, R₂ and R₃ independently represent hydrogen or methyl.

The copolymer resins (formula III to VII) according to the presentinvention can be prepared by a conventional polymerization process suchas bulk polymerization or solution polymerization. Polymerizationinitiators usable in the present invention include benzoyl peroxide,2,2′-azobisisobutyronitrile (AIBN), acetyl peroxide, lauryl peroxide,tert-butyl peracetate, di-tert-butyl peroxide, or the like. As areaction solvent, cyclohexanone, methyl ethyl ketone, benzene, toluene,dioxane and/or dimethylformamide may be used individually, or in amixture.

In the process for preparing the copolymer resin according to thepresent invention, general polymerization condition includingtemperature and pressure of radical polymerization may be controlleddependent upon the property of the reactants, but it is preferable tocarry out the polymerization reaction at a temperature between 60 and200° C. under nitrogen or argon atmosphere for 4 to 24 hours.

The copolymer resin according to the present invention can be used as achemical amplification photoresist, which is prepared by polymerizing(meth)acrylate derivatives in which norbonyl group having a hydrophilicgroup has been introduced to the side chain. The photoresist has highglass transition temperature which is required in the course of themanufacturing process, and has rare absorption at 193 μm, and theprotective group therein can be easily removed. In addition, thenorbonyl group synthesized to have hydrophilicity increasesadhesiveness. The copolymer resin prepared according to the presentinvention can be advantageously used in lithography process, which isexpected to be applied in 1G or 4G DRAM.

The copolymer resin of the present invention can be prepared accordingto a conventional process of photoresist composition, that is, by mixingconventional inorganic acid generator in the presence of organic solventto manufacture photoresist solution. The photoresist can be used in theformation of positive micro-image. In the process for formingphotoresist pattern of semiconductor element, the amount of thecopolymer resin according to the present invention depends on theorganic solvent or inorganic acid generator used, and the condition oflithography, but conventionally it is about 10 to 30% by weight on thebasis of the organic solvent used in the preparation of the photoresist.

The process for forming a photoresist pattern of a semiconductor elementby using the copolymer resin according to the present invention isdescribed in detail here-in-below:

The copolymer resin according to the present invention is dissolved incyclohexanone at a concentration of 10 to 30% by weight. Sulfonium saltor organic sulfonic acid (0.1 to 10% by weight of copolymer resin), asan inorganic acid generator, is added to the copolymer resin solution.The mixture was then filtered with ultra-micro filter to preparephotoresist solution. The inorganic acid generators which can be used inthe process include triphenylsulfonium triplate,dibutylnaphthylsulfonium triplate, 2,6-dimethylphenylsulfonate,bis(arylsulfonyl)diazomethane, oxime sulfonate,2,1-diazonaphthoquinon-4-sulfonate, or the like. The photoresistsolution is spin-coated on a silicon wafer to prepare a thin film, whichis then preheated in an oven or on a heating plate at 80-150° C. for 1-5minutes, exposed to light by using far ultraviolet exposer or an eximerlaser exposer, and post-heated at a temperature between 100° C. and 200°C. for 1 second to 5 minutes. The exposed wafer is impregnated in 2.38%aqueous TMAH solution for 1 to 1.5 minutes to obtain a positivephotoresist pattern.

A better understanding of the present invention may be obtained in lightof following examples which are set forth to illustrate, but are not tobe construed to limit, the present invention.

PREPARATION EXAMPLE I Synthesis of2-tert-butoxycarbonyl-5-hydroxy-6-norbonyl (meth)acrylate

Via Diels-Alder reaction of cyclopentadiene with tert-butylacrylate,2-tert-butoxycarbonyl-5-norbonene was synthesized. Twenty five grams (25g) of 2-tert-butoxycarbonyl-5-norbonene thus prepared was added toacetone (150 ml). After well mixing, the mixture was chilled to −60° C.Potassium permanganate (KMnO₄) (8.15 g) was added in small portions tothe solution, and the reaction was performed at −60° C. for 1 hour.

Then aqueous alkaline solution was slowly added, and the temperature wasslowly raised to reach room temperature. At the same temperature, thereaction was proceeded for 1.5 hours. From the reaction mixture,manganese dioxide was filtered off, and the mixture was washed severaltimes with acetone, and then concentrated by using a rotary evaporatorunder reduced pressure.

The reaction mixture was extracted with dichloromethane, and the extractwas evaporated under reduced pressure. The residue was purified bysilica gel column chromatography to give 22.7 g (yield: 80%) of2-t-butoxycarbonylnorbonan-5,6-diol.

In a 500 ml round-bottomed flask, tetrahydrofuran (100 ml) was charged,and 2-tert-butoxycarbonylnorbonan-5,6-diol (10 g) and triethylamine(13.4 g) were dissolved therein. (Meth)acryloyl chloride (4.6 g) wasslowly added, and the resultant mixture was reacted at −10° C. for 6hours. The reaction mixture was filtered, and evaporated under reducedpressure. The residue was purified by column chromatography to give 9.4g (yield: 72%) of 2-tert-butoxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate.

PREPARATION EXAMPLE II Synthesis of 2-carboxylic-5-hydroxy-6-norbonyl(meth)acrylate

Via Diels-Alder reaction of cyclopentadiene with acrylic acid,5-norbonene carboxylic acid was synthesized.

Twenty grams (20 g) of 5-norbonene carboxylic acid thus prepared wasadded to acetone (150 ml). After well mixing, the mixture was chilled to−60° C.

Potassium permanganate (Kmno₄) (8.15 g) was added in small portions tothe solution, and the reaction was performed at −60° C. for 1 hour. Thenaqueous alkaline solution was slowly added, and the temperature wasslowly raised to reach room temperature. At the same temperature, thereaction was proceeded for 1.5 hours. After filtering off manganesedioxide, the reaction mixture was washed several times with acetone, andthen concentrated by using a rotary evaporator under reduced pressure.The reaction mixture was extracted with dichloromethane, and the extractwas evaporated under reduced pressure. The residue was purified bysilica gel column chromatography to give 14.7 g (yield: 73%) of5-norbonene carboxylic-5,6-diol.

In a 500 ml round-bottomed flask, tetrahydrofuran (100 ml) was charged,and 5-norbonene carboxylic-5,6-diol (8 g) and triethylamine (11.4 g)were dissolved therein. (Meth)acryloyl chloride (3.5 g) was slowlyadded, and the resultant mixture was reacted at −10° C. for 6 hours. Thereaction mixture was filtered, and evaporated under reduced pressure.The residue was purified by column chromatography to give 8.3 g (yield:70%) of 2-carboxylic-5-hydroxy-6-norbonyl (meth)acrylate.

PREPARATION EXAMPLE III Synthesis of2-hydropyranyloxycarbonyl-5-hydroxy-6-norbonyl (meth)acrylate

Via Diels-Alder reaction of cyclopentadiene with hydropyranyl acrylate,2-hydropyranyloxycarbonyl-5-norbonene was synthesized.

Twenty two grams (22 g) of 2-pyranyloxycarbonyl-5-norbonene thusprepared was added to acetone (150 ml). After well mixing, the mixturewas chilled to −60° C. Potassium permanganate (KMnO₄) (7.45 g) was addedin small portions to the solution, and the reaction was performed at−60° C. for 1 hour. Then aqueous alkaline solution was slowly added, andthe temperature was slowly raised to reach room temperature. At the sametemperature, the reaction was proceeded for 1.5 hours. After filteringoff manganese dioxide, the reaction mixture was washed several timeswith acetone, and then concentrated by using a rotary evaporator underreduced pressure. The reaction mixture was extracted withdichloromethane, and the extract was evaporated under reduced pressure.The residue was purified by silica gel column chromatography to give20.6 g (yield: 77%) of 2-hydropyranyloxycarbonylnorbonan-5,6-diol.

In a 500 ml round-bottomed flask, tetrahydrofuran (100 ml) was charged,and 2-hydropyranyloxycarbonylnorbonan-5,6-diol (9 g) and triethylamine(12.1 g) were dissolved therein. (Meth)acryloyl chloride (4.8 g) wasslowly added, and the resultant mixture was reacted at −10° C. for 6hours. The reaction mixture was filtered, and evaporated under reducedpressure. The residue was purified by column chromatography to give 9.8g (yield: 76%) of 2-hydropyranyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate.

PREPARATION EXAMPLE IV Synthesis of2-hydrofuranyloxycarbonyl-5-hydroxy-6-norbonyl (meth) acrylate

Via Diels-Alder reaction of cyclopentadiene with hydrofuranyl acrylate,2-hydrofuranyloxycarbonyl-5-norbonene was synthesized.

Twenty one grams (21 g) of 2-hydrofuranyloxycarbonyl-5-norbonene thusprepared was added to acetone (150 ml). After well mixing, the mixturewas chilled to −60° C. Potassium permanganate (Kmno₄) (7.40 g) was addedin small portions to the solution, and the reaction was performed at−60° C. for 1 hour. Then aqueous alkaline solution was slowly added, andthe temperature was slowly raised to reach room temperature. At the sametemperature, the reaction was proceeded for 1.5 hours. After filteringoff manganese dioxide, the reaction mixture was washed several timeswith acetone, and then concentrated by using a rotary evaporator underreduced pressure. The reaction mixture was extracted withdichloromethane, and the extract was evaporated under reduced pressure.The residue was purified by silica gel column chromatography to give20.1 g (yield: 76%) of 2-hydrofuranyloxycarbonylnorbonan-5,6-diol.

In a 500 ml round-bottomed flask, tetrahydrofuran (100 ml) was charged,and 2-hydrofuranyloxycarbonylnorbonan-5,6-diol (8.8 g) and triethylamine(11.1 g) were dissolved therein. (Meth)acryloyl chloride (4.6 g) wasslowly added, and the resultant mixture was reacted at −10° C. for 6hours. The reaction mixture was filtered, and evaporated under reducedpressure. The residue was purified by column chromatography to give 9.4g (yield: 75%) of 2-hydrofuranyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate.

PREPARATION EXAMPLE V Synthesis of2-ethoxyethyloxycarbonyl-5-hydroxy-6-norbonyl (meth)acrylate

Via Diels-Alder reaction of cyclopentadiene with ethoxyethyl acrylate,2-ethoxyethyloxycarbonyl-5-norbonene was synthesized.

Twenty grams (20 g) of 2-ethoxyethyloxycarbonyl-5-norbonene thusprepared was added to acetone (150 ml). After well mixing, the mixturewas chilled to −60° C. Potassium permanganate (KMnO₄) (7.12 g) was addedin small portions to the solution, and the reaction was performed at−60° C. for 1 hour. Then aqueous alkaline solution was slowly added, andthe temperature was slowly raised to reach room temperature. At the sametemperature, the reaction was proceeded for 1.5 hours. After filteringoff manganese dioxide, the reaction mixture was washed several timeswith acetone, and then concentrated by using a rotary evaporator underreduced pressure. The reaction mixture was extracted withdichloromethane, and the extract was evaporated under reduced pressure.The residue was purified by silica gel column chromatography to give18.1 g (yield: 74%) of 2-ethoxyethyloxycarbonylnorbonan-5,6-diol.

In a 500 ml round-bottomed flask, tetrahydrofuran (100 ml) was charged,and 2-ethoxyethyloxycarbonylnorbonan-5,6-diol (8.5 g) and triethylamine(11.7 g) were dissolved therein. (Meth)acryloyl chloride (5.6 g) wasslowly added, and the resultant mixture was reacted at −10° C. for 6hours. The reaction mixture was filtered, and evaporated under reducedpressure. The residue was purified by column chromatography to give 9.9g (yield: 79%) of 2-ethoxyethyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate.

EXAMPLE I Synthesis of poly[2-tert-butoxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-carboxylic-5-hydroxy-6-norbonyl (meth)acrylate]copolymer resin (Formula III)

In tetrahydrofuran or toluene (25 g),2-tert-butoxycarbonyl-5-hydroxy-6-norbonyl (meth)acrylate (0.05 mol) and2-carboxylic-5-hydroxy-6-norbonyl (meth)acrylate (0.05 mol) weredissolved. Then, 2,2′-azobisisobutyronitrile (AIBN) (0.05 g), as apolymerization initiator, was added thereto, and the reaction wasperformed at 70° C. under nitrogen or argon atmosphere for 4-24 hours.Crude product thus obtained was precipitated from ethyl ether or hexane,and the precipitate was dried to give 23.2 g (yield: 89%) of the titlecopolymer resin (Formula III) having molecular weight of 4,000-100,000.The copolymer resin thus prepared, as a chemically amplifiable resisthaving increased adhesiveness and sensitivity of photoresist, has highglass transition temperature required in the course of the process, andrare absorption in far ultraviolet region, in particular, at 193 μm. Theprotective group can be easily removed from the copolymer resin, and theresin is able to form a 0.15 μm pattern in practical patterningexperiment.

EXAMPLE II Synthesis of poly[2-tert-butoxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-hydroxyethyl (meth)acrylate/(meth)acrylic acid]copolymer resin (Formula IV)

In tetrahydrofuran or toluene (25 g),2-tert-butoxycarbonyl-5-hydroxy-6-norbonyl (meth)acrylate (0.05 mol),2-hydroxyethyl (meth)acrylate (0.04 mol) and (meth)acrylic acid (0.01mol) were dissolved. Then, 2,2′-azobisisobutyronitrile (AIBN) (0.04 g),as a polymerization initiator, was added thereto, and the reaction wasperformed at a temperature between 65° C. and 70° C. under nitrogen orargon atmosphere for 4-24 hours. Crude product thus obtained wasprecipitated from ethyl ether or hexane, and the precipitate was driedto give 21 g (yield: 83%) of the title copolymer resin (Formula IV)having molecular weight of 4,000-100,000. The copolymer resin thusprepared has similar properties to the copolymer obtained in Example I,and the resin is able to form a 0.14 μm pattern in practical patterningexperiment.

EXAMPLE III Synthesis ofpoly[2-hydropyranyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-hydroxyethyl (meth)acrylate/(meth)acrylic acid]copolymer resin (Formula V)

In tetrahydrofuran or toluene (20 g),2-hydroxypyranyloxycarbonyl-5-hydroxy-6-norbonyl (meth)acrylate (0.07mol), 2-hydroxyethyl (meth)acrylate (0.02 mol) and (meth)acrylic acid(0.01 mol) were dissolved. Then, 2,2′-azobisisobutyronitrile (AIBN)(0.04 g), as a polymerization initiator, was added thereto, and thereaction was performed at a temperature between 65° C. and 70° C. undernitrogen or argon atmosphere for 4-24 hours. Crude product thus obtainedwas precipitated from ethyl ether or hexane, and the precipitate wasdried to give 26 g (yield: 81%) of the title copolymer resin (Formula V)having molecular weight of 4,000-100,000.

The copolymer resin thus prepared, in which the protective group theresin prepared in Example 2 was changed by acetal group, is an excellentcopolymer resin having increased sensitivity without deterioratingetching resistance (sensitivity: 100 mJ/cm²).

EXAMPLE IV Synthesis ofpoly[2-hydrofuranyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-hydroxyethyl (meth)acrylate / (meth)acrylic acid]copolymer resin (Formula VI)

In tetrahydrofuran or toluene (20 g),2-hydrofuranyloxycarbonyl-5-hydroxy-6-norbonyl (meth)acrylate (0.07mol), 2-hydroxyethyl (meth)acrylate (0.02 mol) and (meth)acrylic acid(0.01 mol) were dissolved. Then, 2,2′-azobisisobutyronitrile (AIBN)(0.04 g), as a polymerization initiator, was added thereto, and thereaction was performed at a temperature between 65° C. and 70° C. undernitrogen or argon atmosphere for 4-24 hours. Crude product thus obtainedwas precipitated from ethyl ether or hexane, and the precipitate wasdried to give 25 g (yield: 80%) of the title copolymer resin (FormulaVI) having molecular weight of 4,000-100,000. The copolymer resin thusprepared has similar properties to the copolymer obtained in ExampleIII.

EXAMPLE V Synthesis ofpoly[2-ethoxyethyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-hydroxyethyl (meth)acrylate/(meth)acrylic acid]copolymer resin (Formula VII)

In tetrahydrofuran or toluene (20 g),2-ethoxyethyloxycarbonyl-5-hydroxy-6-norbonyl (meth)acrylate (0.07 mol),2-hydroxyethyl (meth)acrylate (0.02 mol) and (meth)acrylic acid (0.01mol) were dissolved. Then, 2,2′-azobisisobutyronitrile (AIBN) (0.04 g),as a polymerization initiator, was added thereto, and the reaction wasperformed at a temperature between 65° C. and 70° C. under nitrogen orargon atmosphere for 4-24 hours. Crude product thus obtained wasprecipitated from ethyl ether or hexane, and the precipitate was driedto give 20 g (yield: 81%) of the title copolymer resin (Formula VII)having molecular weight of 4,000-100,000. The copolymer resin thusprepared has similar properties to the copolymer obtained in ExampleIII, but it is more excellent in view of contrast.

EXAMPLE VI

One of the copolymer resin (Formula III to VII) (10 g) obtained inExample 1 to 5 was dissolved in 3-methoxymethyl propionate (40 g,solvent), and sulfonium triplate or dibutylnaphthylsulfonium triplate(about 0.2-1 g) as an inorganic acid generator, was added thereto. Afterstirring, the mixture was filtered to give a photoresist solution. Thenthe photoresist solution was spin-coated on a surface of a wafer toprepare thin film, and the wafer was preheated in an oven of 70-150° C.or on a hot plate for 1-5 minutes. After exposing to light of 250 nmwavelength by using an exposer, it was post-heated at 90-160° C. Then,the exposed wafer was impregnated in an aqueous TMAH solution having aconcentration of 0.01-5% by weight as a developing solution, for 1.5minutes to obtain ultra-micro photoresist pattern (resolution: 0.15 μm).

The copolymer resin according to the present invention is easilyprepared by conventional radical polymerization due to the introductionof norbonyl(meth)acrylate unit to a structure of copolymer forphotoresist. The resin has high transparency at 193 nm wavelength,provides increased etching resistance and enhanced adhesive strength dueto a hydrophilic functional group in the norbonyl group, and showsexcellent resolution of 0.15 μm.

Many modifications and variations of the present invention are possiblein light of the above teachings. Therefore, it is to be understood thatwithin the scope of the appended claims, the invention may be practicedotherwise than as specifically described.

What is claimed is:
 1. A copolymer resin which comprises5-hydroxy-6-norbornyl(meth)acrylate unit represented by formula II:

wherein, R represents 2-tert-butoxycarbonyl, 2-carboxyl,2-hydropyranyloxycarbonyl, 2-hydrofuranyloxycarbonyl or2-ethoxyethyloxycarbonyl, and R₁ represents hydrogen or methyl.
 2. Acopolymer resin in accordance with claim 1, which ispoly[2-tert-butoxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-carboxylic-5-hydroxynorbornyl-6-(meth)acrylate]copolymerresin represented by formula III;

wherein R₁ and R₂ independently represent hydrogen or methyl, and x, yand z independently represent mole fraction between 0.001 and 0.99.
 3. Acopolymer resin in accordance with claim 1, which ispoly[2-tert-butoxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-hydroxyethyl(meth)acrylate/(meth)acrylic acid]copolymer resin represented by formulaIV;

wherein R₁, R₂ and R₃ independently represent hydrogen or methyl, and x,y, and z independently represent mole fraction between 0.001 and 0.99.4. A copolymer resin in accordance with claim 1, which ispoly[2-hydroxypyranyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-hydroxyethyl(meth)acrylate/meth)acrylicacid]copolymer resin represented by formula V;

wherein R₁, R₂ and R₃ independently represent hydrogen or methyl, and x,y, and z independently represent mole fraction between 0.001 and 0.99.5. A copolymer resin in accordance with claim 1, which ispoly[2-hydroxyfuranyloxycarbonyl-5-hydroxy-6-norbonyl(meth)acrylate/2-hydroxyethyl(meth)acrylate/(meth)acrylicacid]copolymer resin represented by formula VI;

wherein R₁, R₂ and R₃ independently represent hydrogen or methyl, and x,y, and z independently represent mole fraction between 0.001 and 0.99.6. A copolymer resin in accordance with claim 1, which ispoly[2-ethoxyethyloxycarbonyl-5-hydroxy-6-norbornyl(meth)acrylatel2-hydroxyethyl(meth)acrylate/(meth)acrylicacid]copolymer resin represented by formula VII;

wherein, R₁, R₂ and R₃ independently represent hydrogen or methyl, andx, y, and z independently represent mole fraction between 0.001 and0.99.